1. Field
The present invention relates to communications of data, and more particularly to communications for accessing supplementary services with a multi-mode wireless device.
2. Background
Supplementary services are widely used in wireless networks. Supplementary services (known as “cellular features” in CDMA and TDMA specifications), such as call forwarding, call waiting, call barring, etc., enhance the basic voice call services of typical wireless service plans. Supplementary services are accessed by service codes and man-machine interface (MMI) procedures. A service code is a special phone number composed of 0, 1, . . . 9, * and # with a predefined format according to each of the wireless system standards. For example, in CDMA, to implement call forwarding, the user enters the digit string “*68”, and then presses the SEND or TALK key to originate a call to the network with that digit string. Each type of wireless system has unique service codes. These service codes and MMI procedures standardize the process for sending requests to the network to activate, deactivate, interrogate, register, or erase one or more of the supplementary services. If a particular supplementary service is active, a user invokes a network-specific procedure to enable the service, such as forwarding an incoming call for example.
A problem arises for users of a multi-mode wireless device, i.e. a wireless device compatible for operations with more than one wireless system. Since different wireless systems employ distinct service codes and MMI procedures, a user would need to know what system is currently being used by the wireless device. Further, if one wireless system becomes out of range or otherwise fails for any reason and a different wireless system is used during the process, the steps already made for supplementary services are not guaranteed to be accepted by the new wireless system.